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Appendix IIL





P. 600. Value of Joule's equivalent.  Rowland has
repeated Joule's experiment of the churning of water, but on a
much larger scale and for a longer time, driving the paddles by
motive power and measuring the energy with a dynamometer.
The much larger values thus obtained produce a greater
approach to accuracy, and the altered value of J = 778 is
now pretty universally accepted, Osborne Reynolds has since
reviewed all known experiments, including those of Joule, and
by careful correction deduces a result closely approximating to
that of Rowland. As the correction is an increase of only '515
of one per cent, the values within this book have not been
altered. (Seep. 1130.)

Now, on p. 603, Cv is deduced from Cp when J is known ;
conversely J may be found if 7 is obtainable directly. This is not
impossible, though difficult to do accurately. In books on
physics we find

velocity ot        I   _     /  fr
sound in air at 32 j    ~~   vV"-

where g    32*2       and H = PV = 26214    -(? 59)
Hence y =   1-408     and Cv =   = ~~| = '167

Now Kp~Kv = c ...... . .............................. (p. 604)

and -g = 7

also ^ =  53'28


.    K

.(p. 603)
(P- 59o)

p ~ Kp-Kv


J  -



-i   C

Prof.   Thurston has pointed  out a curious though totally
unexplained coincidence, viz. that most probably